The invention relates to displays, and more particularly, to a high-reliability lighting system that provides light to a display.
A common type of visual display includes a light source, such as an arc lamp, that is modulated to provide a readable output for a user. Displays used in applications such as avionics must be designed to operate even if the light source fails. Consequently, high-reliability displays have a back-up light source that is actuated if something is wrong with the principal lighting source. Because of space considerations such a back-up light source may have a smaller, lesser-intensity bulb. Alternately, the back-up light source may light only part of the display, which may cause a reduction in quality of the readable output.
Another issue relating to displays is that some types of displays require an output to have a specific polarization state or direction. As is known in the art, polarized light may be defined as being in one of two orthogonal polarization states or orientations, known as the p and s polarization states, that are both orthogonal to the direction of transmission of light. A display may require light to be in either the p or the s polarization state. It is difficult to properly maintain the desired polarization direction in a lighting system with multiple light sources, especially when the light sources can be actuated in any one of several combinations.
It is therefore an object of the invention to provide a lighting system that may be operated in a high-reliability environment.
It is another object of the invention to provide a high-reliability lighting system that maintains a consistent output even in the event of failure.
It is still another object of the invention to provide a high-reliability lighting system that provides light with a consistent polarization state regardless of the combination of light sources that are actuated therein.
A feature of the invention is the use of optically reflective and transmissive elements that combine the polarized light from a plurality of lamps so that the polarization state of the light so produced may be modified as desired.
An advantage of the invention is that a compact, high-reliability source of polarized light is ensured.
The invention provides a lighting system that includes a first selectively actuated light module that emits light having a first polarization orientation. A second selectively actuated light module emits light having a second polarization orientation that is orthogonal to the first polarization orientation. A first combining element combines and directs light from the first and second light modules into an optical path. A first polarization alignment element aligns the polarization of light from the first combining element to a predetermined polarization orientation. The first and second light modules are selectively actuated to ensure that light having the predetermined polarization orientation is substantially constantly emitted when desired.
The invention also provides a lighting system including a first selectively actuated light module that emits light having a first polarization orientation. A second selectively actuated light module emits light having a second polarization orientation that is orthogonal to the first polarization orientation. A third selectively actuated light module emits light having the first polarization orientation. A first combining element combines and directs light from the first and second light modules into a first optical path. A first polarization alignment element aligns the polarization of light from the first combining element to a first predetermined polarization orientation. A second combining element combines light from the third light module with light from the first and second light modules. A second polarization alignment element aligns the polarization of light from the second combining element to a second predetermined polarization orientation. The first, second and third light modules are selectively actuated to ensure that light having the second predetermined polarization orientation is substantially constantly emitted when desired.
The invention further provides a method of providing a source of light. According to the method, light from a first light module with a first polarization orientation is selectively provided. Light from a second light module with a second polarization orientation that is orthogonal to the first polarization orientation is selectively provided. Light from the first and second light modules are combined and directed into an optical path. The polarization of light in the optical path is aligned to a predetermined polarization orientation. Light from the first and second light modules is selectively emitted to ensure that light having the predetermined polarization is substantially constantly emitted when desired.